A biracial population of over 800 young adults, ages 25-35, from the Oakland, California center of the CARDIA research study will be recruited to participate in a cross-sectional study of bone density to be performed at the next CARDIA exam from June 1992-May 1993. CARDIA (acronym for Cardiovascular Risk Development in Young Adults) is an NHLBI-funded study of risk factors for cardiovascular disease in young adults; the CARDIA study population is approximately equally distributed among blacks and whites, men and women. The cross-sectional relationship of the following known or suspected covariates to bone density will be analyzed in 701 subjects: age, body mass index, percent body fat, lean body mass, dietary calcium intake, physical activity, cigarette smoking, alcohol consumption, and oral contraceptive use. Serum levels of calciotropic hormones, sex hormones, growth factors and indicators of bone formation/resorption will be measured in 400 subjects in order to characterize race-sex differences and explore relationships of these measurements with bone density and the covariates of bone density. Total body calcium, spinal and femoral bone density will be measured with dual energy radiography (Hologic QDR-200 bone densitometer). The CARDIA study will provide funding for several of the measurements, some of which will be available not only for the time of bone mass measurements, but as far back as 7 years earlier (e.g. body mass index, dietary calcium intake, physical activity). This study represents a unique opportunity to compare potential determinants of bone density for each race and sex group and to analyze what factors account for race and sex differences in skeletal metabolism at the time peak bone mass is achieved. Since bone mass in early adulthood is believed to account for race and sex differences in the risk of osteoporotic fracture later in life, this study should increase knowledge of factors that may influence the future development of osteoporosis. By identifying sex and racial differences in skeletal physiology, this research could characterize those mechanisms responsible for control of skeletal density.